The reason is simple: they're both wrong. The only difference is that there's a social movement which one is (sometimes) aligned with that (except when it's not) that props them up.
Thomson didn't have any ideological support behind him, he was simply anti-video games with nothing other then generic "anti-violence" as his call.
Anita, on the other hand, has the more radical parts of the modern feminist movement behind her. Apart from the movement (which having is always very helpful) the only difference between them is how blatantly a con they both where, with Thomson being of a lesser degree. They had much in common after all, both being people who never where into video games nor had any interest in starting to play them, but still wanted them censored and changed to suit their image of how it should be.
Off topic: when are Running with Scissors going to make a Postal 2 equivalent for Anita? Say what you will about that game, it was beautiful in it's decadence, and we owe it all to good, hard working developers wanting to give the finger to Thomson.